FR2952124A1 - METHOD AND DEVICE FOR MONITORING AN EXHAUST GAS CLEANING INSTALLATION - Google Patents

Abstract

Method for monitoring an exhaust gas cleaning system emitted by a heat engine (1), composed of a catalyst (70) for converting and / or accumulating at least one component of the exhaust gases of the heat engine ( 1), the catalyst is an oxidation catalyst. According to the method, using the adsorption capacity of at least partially unburned hydrocarbons of the catalyst (70), a predictive diagnosis of the NO oxidation capacity of the catalyst (70) is deduced. The at least partially unburned hydrocarbons are at least partly introduced in a targeted manner upstream of the catalyst (70) in the exhaust gas channel (50).

Description

FIELD OF THE INVENTION The present invention relates to a method for monitoring an exhaust gas cleaning system emitted by a heat engine, composed of one or more catalysts for converting and / or accumulating at least one component of the gases. exhaust of the heat engine, these catalysts being installed in the exhaust gas channel of the engine, and at least one of the catalysts being an oxidation catalyst. The invention also relates to a device for implementing such a method. To reduce the pollutant components of the exhaust gases emitted by heat engines, it is known to install catalyst systems comprising at least one catalyst in the exhaust gas channel of the engine.

Depending on the type of catalyst, one or more components of the exhaust gases such as unburned hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NO) are converted into less polluting products. Catalysts having accumulation components for adsorbing certain particular pollutants are also known. Thus, in particular, in the case of lean-mode heat engines, non-nitrogen oxide storage catalysts are used which adsorb in the lean operating phases for> 1 NO oxides and provide reduction of NO accumulated nitrogen oxides in the rich, intermediate regeneration phases for X <1. Practically for all catalyst systems, during operation, there are more or less marked collapses of the conversion capacities and / or accumulation with respect to the initial activity of the catalyst. Conversion or accumulation activities can be damaged by different poisons. In particular, in the case of nitrogen oxide accumulator catalysts NO, various poisoning units are known, leading, for example, to a significant neutralization of the conversion of nitrogen oxides, although the HC conversion is still good. We also know exactly the opposite behavior.

2 The most rigorous legislation in the field of diagnostics of emission components requires, in the context of on-board diagnostics (OBD diagnostics), the monitoring of all aftertreatment components of the exhaust gases as well as the sensors used. vis-à-vis the OBD limit which is usually a multiple of the emission limit. Catalyst monitoring is a particularly important challenge. According to the state of the art, a large number of different methods for diagnosing exhaust gas aftertreatment systems are already known. DE 41 12 478 C2 discloses, for example, a method for assessing the aging state of a catalyst according to which the Lambda values are measured upstream and downstream of the catalyst. It is examined whether for a control oscillation upstream of the catalyst passing from the rich mode to the lean mode or vice versa, the Lambda coefficient downstream of the catalyst has a corresponding variation; if this is the case, the mass flow rate of gas passing through the catalyst is determined. This flow rate is the integral as a function of time of the product of the mass flow rate of gas and the Lambda coefficient upstream of the catalyst; the integral as a function of time of the product of the mass flow rate of the gas and the Lambda coefficient downstream of the catalyst is calculated; the difference between the two integrals thus calculated or the coefficient of the two integrals or the coefficient of the difference of the two integrals divided by one of the two integrals is used as a measure of the degree of aging of the catalyst. The disadvantage of this described method is that the Lambda coefficient must be measured upstream of the exhaust gas installation with a broadband Lambda probe, which is an expensive probe, to allow the amount of oxygen introduced to be determined. or taken by the integration of the product of the current Lambda coefficient and the mass flow rate of gas. Document DE 198 03 828 A1 describes a method and a device for controlling the monitoring of an exhaust gas catalyst fitted to thermal engines according to which the oxygen content of the exhaust gases downstream of the engine is determined.

3 catalyst and modifies the average oxygen content of the exhaust gas upstream of the catalyst in the sense of removing the oxygen content determined beforehand, downstream of the catalyst; from the variation of the average oxygen content, the resulting variation of the oxygen filling level of the catalyst is determined; it is compared to a predefined limit value but there is no fault signal if the preset limit is exceeded before the oxygen content of the exhaust gas downstream of the catalyst changes.

Document DE 10 2006 041479 A1 describes another method for determining the oxygen storage capacity of an engine exhaust gas cleaning system according to which the difference between a quantity of oxygen supplied is determined. at the exhaust cleaning plant and an amount of oxygen extracted from the exhaust cleaning plant to form the oxygen filling level of the exhaust gas cleaning plant at the from the difference of the two quantities. Even if the oxygen is not completely exhausted, or if the catalyst is filled with oxygen, it is possible to start a measurement cycle and indicate whether the catalyst has sufficient conversion capacity. In addition, an oxygen passage can be taken into account in the case of an exhaust gas cleaning installation that is not completely filled, that is to say, to take account of the slippage.

Current requirements for on-board diagnostics, particularly as known in the United States, require, for example, the monitoring of oxidation catalysts, for example Diesel oxidation catalysts (DOC catalysts) to determine their ability to ensure an appropriate conversion of exhaust gas, that is to say by supplying a feed gas to the aftertreatment system of the exhaust gas. The objective is to ensure a defined NO / NO2 ratio for the reduction of nitrogen oxides NO. can be performed under optimal conditions in the downstream SCR catalyst. SCR catalyst is a catalyst with selective catalytic reduction. This is the technique of reduction

4 catalytic selective nitrogen oxides contained in the exhaust gases of heating installations, waste incineration plants, gas turbines, industrial plants and engines. The chemical reaction at the level of the SCR catalyst is selective; this means that the nitrogen oxides (NO, NO2) are preferentially reduced whereas the unwanted side reactions (for example the oxidation of sulfur dioxide to sulfur trioxide) are very largely blocked. There are two types of catalyst. One of the types consists mainly of using titanium dioxide, vanadium pentoxide and tungsten oxide. The other type uses zeolites. Another requirement relates to the monitoring of the coating of a diesel particulate filter (also called DPF filter) as to its ability to oxidize unburned hydrocarbons (HC).

The currently known method does not meet all the requirements for monitoring. Thus, it is not possible, for example, to exploit the NO oxidation capacity of a Diesel Oxidation Catalyst (DOC) using the conversion capacity HC because the oxidation capacity NO decreases more rapidly, that is, it ages faster and no longer allows for proper correlation between the two properties. If, on the other hand, it is sought to monitor the DPF coating by the exothermic process known as the Diesel Oxidation Catalyst (DOC), it fails because of the small amount of HC hydrocarbons which, under normal conditions, arrives in the Diesel Particulate Filter (DPF) downstream of the Diesel Oxidation Catalyst. OBJECT OF THE INVENTION The present invention aims to develop a method for reliably and better monitoring a catalyst, especially an oxidation catalyst to determine the NO oxidation capacity. Another object of the invention is to develop a device for implementing such a method. DESCRIPTION OF EMBODIMENTS OF THE INVENTION To this end, the invention relates to a method of the type defined above, characterized in that, by means of the adsorption capacity of at least partially unburned hydrocarbons of a catalyst, a predictive diagnosis of the NO oxidation capacity of the catalysts is deduced, the at least partially unburned hydrocarbons being at least less partly introduced in a targeted manner upstream of the catalysts in the exhaust gas channel.

The invention also relates to a device of the type defined above, characterized in that with the aid of a diagnosis unit connected at the input, exhaust gas sensors, and at least one temperature sensor. in order to determine the temperature or the temperature increase and / or to an HC sensor for determining the partially unburned hydrocarbons, downstream of the oxidation catalyst and with the aid of the signals of the diagnostic unit, a provisional diagnosis is deduced the NO oxidation capacity of the catalysts, the partially unburned hydrocarbons being introduced at least from time to time in a targeted manner upstream of the catalysts in the exhaust gas channel, where appropriate using specific metering means ordered by the diagnostic unit. The process according to the invention uses the adsorption capacity of hydrocarbons (HC) by catalysts as indicators of their poisoning, for example as a result of a thermal overload. The state of this indicator makes it possible to know the capacity to monitor the catalysts which make it possible to oxidize NO oxides. This method and the device for its implementation make it possible to determine the NO oxidation capacity of the catalysts preserved in the context of the more stringent requirements relating to on-board diagnostics 3o as to the capacity to supply such "feed gas" to the systems aftertreatment of downstream exhaust gases. According to a characteristic of the process, the adsorption capacity of the unburned hydrocarbons is determined by means of the amplitude of the increase of the temperature.

6 and / or a temperature level reached during the combustion of the quantity of hydrocarbons introduced. This exotherm is released if the previously introduced hydrocarbons are again desorbed from a certain temperature and then burned on the noble metal coating of the oxidation catalyst with the oxygen contained in the exhaust gas. Another possibility of detecting partially burned hydrocarbons is to use at least one HC sensor installed behind the catalyst in the direction of passage of the exhaust gas. This makes it possible to directly detect the passage of a quantity of HC hydrocarbons. According to another characteristic, for the diagnosis, a defined amount of hydrocarbons is introduced upstream of the catalyst operating as an oxidation catalyst until a hydrocarbon cross-over is detected with the HC sensor, the operation being carried out. below the temperature at which the oxidation catalyst has a significant efficiency for the conversion of hydrocarbons. This temperature is also called "ignition temperature or trip temperature". At this temperature, the conversion coefficient significantly exceeds 50%. The trip temperature is approximately 250 ° C depending on the type of pollutant in the case of gasoline engines. In the case of operation as a diesel engine, the trip temperature is below 200 ° C. The triggering temperature is however not a constant value but increases with aging of the catalyst. In addition, the trigger temperature is different according to the reactions and thus according to the different types of pollutants.

Alternatively, the degree of desorption of the hydrocarbons is measured by an input of enthalpy upstream of the oxidation catalyst by the HC sensor and this correlation is correlated with the activity of the oxidation catalyst. As the accumulation ability of HC hydrocarbons, instant, aging-related and also the oxidation activity of

7 age-old noble metals must be chemically tuned to one another, that is to say, to be correlated, the catalytic coating of the oxidation catalyst will be monitored for its oxidation capacity nitrogen oxides NO and its robustness and reliability to meet the regulations. According to a characteristic of the process, the quantity of hydrocarbons introduced for the diagnosis is made using a separate HC hydrocarbon dosing system in the exhaust gas channel upstream of one of the catalysts. Post-injection allows a sufficiently large amount of unburnt hydrocarbons to enter the exhaust channel. According to another feature, as a variant or in combination, the quantity of hydrocarbons introduced for diagnosis is made using a separate metering facility HC, in the exhaust gas channel upstream of one catalysts. The hydrocarbon feed can be directly upstream of the diagnostic catalyst components. The cold start phase of the engine is another possibility for the diagnostic space, according to which the quantity of hydrocarbons introduced for the diagnosis is done at cold start of the engine. Particularly in this phase, the exhaust gases contain a high content of partially burned hydrocarbons. According to a preferred characteristic, if a threshold of the hydrocarbon accumulation capacity or of a characteristic correlated thereto is exceeded, a critical activity is recorded for the NO oxidation capacity and emits a warning signal and / or is stored in a fault memory of a motor control. This allows for an on-board diagnostic, complying with the regulations. A preferred application of the process described above in these various aspects is its application to a diesel particulate filter for detecting the conversion capacity using the HC hydrocarbon storage capacity in the case of a coating. Diesel particulate filter.

According to one characteristic, the diesel particulate filter is combined with an upstream oxidation catalyst (Diesel DOC oxidation catalyst). It is intended to introduce a sufficiently large amount of HC hydrocarbons into the assembly consisting of the oxidation catalyst and a diesel particulate filter coated with a catalyst, sufficient to also store hydrocarbons in the coating of the particulate filter. Diesel downstream of the oxidation catalyst. By determining the thermal orientation by the oxidation catalyst and, where appropriate, more by the coating of the diesel particulate filter or the HC hydrocarbon desorption rate by the HC sensor after the oxidation catalyst and after the coating of the diesel particulate filter, one can also monitor the oxidation capacity of the diesel particulate filter. The aging of the hydrocarbon accumulation material HC is defined as a function of the expected aging of the coating of the diesel particulate filter. Another advantage results from the application of the process according to which the quantity of HC hydrocarbons accumulated and which at temperatures lower than the ignition temperature of the diesel oxidation catalyst have been accumulated on it will be used. at a later time, that is to say when the hydrocarbons are at least partially desorbed from this diesel oxidation catalyst, to exploit the oxidation capacity of the coating of the diesel particulate filter downstream. For an appropriate design of the HC hydrocarbon storage capacity of this diesel oxidation catalyst, it will be possible for desorption HC, desired, not to burn in the diesel oxidation catalyst, the hydrocarbons thus released, but to transfer them. to the coating of the diesel particulate filter downstream and burn them there or store them again intermediately. The combustion can be exploited as already described above, by exploiting the exothermic effect. This new intermediate storage can be achieved by exploiting the HC hydrocarbon storage capacity of the diesel particulate filter coating or HC slip. The exploitation of the HC storage capacity can also be used in a diesel particulate filter coating

9 as an indicator for other coating functions such as the NO oxidation capacity. A particular variant of the device is characterized in that at least one of the catalysts comprises at least one accumulation component for partially unburned hydrocarbons and this component is in zeolites. And the hydrocarbon storage capacity is reduced to temperatures at which the noble metal sintering of the oxidation catalyst begins. This can be done for example by hydrothermal destruction of zeolites.

The adjustment of the storage capacity can be adjusted according to the sintering temperature of the noble metals, specifically by adjusting the variation of the silicon / aluminum ratio and / or the type of zeolites. According to another development, at least one of the catalysts additionally comprises oxygen storage components (oxygen storage capacity OSC), such as, for example, ceroxides, CR / zircon mixed oxides and / or praseodymium and / or neodymium oxide. These can be correlated for their aging behavior, i.e., their ability to accumulate decreasing oxygen as a function of aging, with the sintering of noble metals. In combination with the hydrocarbon storage capacity, two potential hydrocarbon consumption characteristics, namely the direct accumulation of HC hydrocarbons and a reaction consumption of the hydrocarbons with the OSC material, are combined or combined. allows to increase all the sensitivity of the process. For a new oxidation coating having HC storage materials and OSC materials, compared with an aged coating, there will be a greater exothermic effect for the introduction of a defined amount of HC hydrocarbons, which as described above, is introduced and / or a smaller amount of HC hydrocarbons up to the HC hydrocarbon flow effect that is observed and measured downstream of the catalyst. This difference can be correlated with the NO oxidation capacity of the coating.

Drawings The present invention will be described hereinafter in more detail with the aid of an exemplary embodiment shown in the accompanying drawings in which: - Figure 1 is a schematic view of the technical environment in which the method of the invention, - Figure 2 shows an alternative technical environment in which the method according to the invention applies. DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION FIG. 1 shows by way of example the technical environment in which the method according to the invention applies. The representation is limited to the essential components for the presentation of the invention. Figure 1 shows a heat engine 1 composed of a motor block 40 and an air supply channel 10 which supplies the engine block 40 with combustion air; the quantity of air in the air intake duct 10 is determined by a supply air measurement installation 20. The exhaust gases emitted by the heat engine 1 arrive in a gas cleaning installation. exhaust having as main component, an exhaust gas channel 50. Depending on the direction of passage of the exhaust gas, the channel comprises a first exhaust gas sensor 60, a Lambda probe for determining the oxygen content in upstream of the catalyst 70 and, if appropriate, a second oxygen sensor 90, another Lambda probe downstream of the catalyst 70. The exhaust gas sensors 60, 90 are connected to a motor control 140 (control electronics engine), which receives the exhaust gas sensor data 60, 90 and those of the air supply meter 20 for calculating the mixture and controlling the fuel metering system 30 for metering the fuel. added. A diagnostic unit 150 is coupled to the motor control 140 or is integrated therein. The metering unit makes it possible to exploit the signals of the exhaust gas sensors 60, 90. The diagnostic unit 150 can be connected to the not shown display / storage unit. 10

With the aid of the engine control 140, a value of the Lambda coefficient can be set with the exhaust gas sensor 60 installed downstream of the engine block 40 in the exhaust gas channel 50. The Lambda coefficient thus set allows the exhaust cleaning system to achieve its optimum cleaning effect. The second exhaust gas sensor 90 installed in the exhaust gas channel 50 downstream of the catalyst 70 can also be operated in the engine control 140 and is used to determine the oxygen storage capacity in the engine. the exhaust gas cleaning system in a method according to the state of the art. The catalyst 70 can be, for example, a 3-way catalyst which ensures both the oxidation of unburned hydrocarbons (HC) and carbon monoxide (CO) and also the catalytic reduction of NO oxides. The catalyst may also be connected to an accumulation component, for example for nitrogen oxides, so as to store nitrogen oxides NO. in the lean mode operating phases (X> 1) and to restore them, to convert them into the operating phases in rich mode (X <1).

To monitor the temperature of the catalyst according to the example shown, behind the catalyst 70 in the direction of passage of the exhaust gas, the exhaust gas channel 50 comprises a temperature sensor 100. This sensor is also connected to the control motor 140 to exploit the temperature signals.

According to the invention, for the diagnosis of the NO oxidation capacity of the catalyst 70, it is provided that with the aid of the hydrocarbon adsorption capacity (HC) at least partially unburned, the catalyst provides a diagnosis of the NO oxidation capacity and the partially unburned hydrocarbons are at least partly introduced in a targeted manner upstream of the catalyst 70 in the exhaust gas channel 50. In the example presented, this is done by a post fuel injection; the fuel metering system 30 receives corresponding control signals from the diagnostic unit 150 from the engine control 140. The adsorption ability of partially unburned hydrocarbons can be

12 using the magnitude of the increase in temperature or temperature level achieved using the temperature sensor 100 during the combustion of the amount of hydrocarbon introduced. Figure 2 shows, as in Figure 1, another embodiment of the technical environment. In this figure, the same references as in the previous figure have been used to designate the same elements. Unlike the assembly of FIG. 1, the heat engine 1, the exhaust gas channel 50 of which is equipped with two catalysts, comprises a precatalyst 80 near the engine in the form of a 3-way catalyst and a main catalyst 110. in place of the main catalyst 110, a particulate filter 120 (DPF) having a catalytic coating can also be provided. The precatalyst 80 is constituted in this case in the form of a diesel oxidation catalyst (DOC catalyst). According to the process, in this example, a sufficiently large quantity of hydrocarbons is introduced into the precatalyst 80 designed as a Diesel Oxidation Catalyst (DOC) and in the catalytically coated Diesel Particulate Filter 120; this amount is sufficient to store hydrocarbons in the coating of the particulate filter downstream of the oxidation catalyst. By determining the thermal tone by the oxidation catalyst and, if appropriate, additionally by the coating of the diesel particulate filter which is measured by means of the temperature sensor 100, or by the HC hydrocarbon desorption coefficient, which it is measured using an HC 130 sensor downstream of the diesel particulate filter 120, it is possible to monitor the oxidation capacity of the diesel particulate filter 120. The quantity of HC hydrocarbons is introduced in this example using a separate metering facility HC 160, which injects fuel upstream of the precatalyst 80 made as a diesel oxidation catalyst (DOC) in the exhaust gas channel 50. This installation of HC 160 dosing is also controlled by the motor control 140 from the diagnostic unit 150.

The process and the device for carrying out the process according to the invention make it possible to exploit the oxidation capacity of the catalysts concerned in the context of the extensive requirements relating to on-board diagnostics as regards the capacity to supply a "feed gas". "downstream aftertreatment systems. 15 NOMENCLATURE OF MAIN ELEMENTS

10 feed channel 20 air metering system 30 fuel metering system 40 engine block 50 exhaust gas channel 60 exhaust gas sensor 70 catalyst 80 precatalyst 90 exhaust gas sensor 100 air flow sensor temperature 110 main catalyst 120 particulate filter Diesel 130 hydrocarbon sensor 140 motor control 150 diagnostic unit 160 hydrocarbon dosing system20

Claims (1)

CLAIMS 1 °) A method of monitoring an exhaust cleaning plant emitted by a heat engine (1), composed of one or more catalysts (70, 80, 110) to convert and / or accumulate at least one s component of the exhaust gas of the heat engine (1), these catalysts being installed in an exhaust gas channel (50) of the heat engine (1), at least one of the catalysts being an oxidation catalyst, characterized in that using the adsorption capacity of at least partially unburned hydrocarbons of a catalyst (70, 80, 110), a predictive diagnosis of the NO oxidation capacity of the catalysts is deduced ( 70, 80, 110), the at least partially unburned hydrocarbons being at least partly introduced in a targeted manner upstream of the catalysts (70, 80, 110) in the exhaust gas channel (50). Process according to Claim 1, characterized in that the adsorption capacity of the partially unburned hydrocarbons is determined by means of the magnitude of the increase in temperature and / or the temperature level attained at during the combustion of the quantity of hydrocarbons introduced. The method of claim 1, characterized by at least one HC sensor (130) for detecting partially unburned hydrocarbons downstream of the catalyst (s) (70, 80, 110) in the direction of passage of the exhaust gas. 4. Process according to claim 3, characterized in that for the diagnosis a defined amount of hydrocarbons is introduced upstream of the catalyst (70, 80, 110) operating as an oxidation catalyst until a hydrocarbon crossing 16 is detected with the HC sensor (130), the operation being below the temperature at which the oxidation catalyst has a significant efficiency for hydrocarbon conversion. Process according to Claim 3 or 4, characterized in that the degree of desorption of the hydrocarbons is measured by an input of enthalpy upstream of the oxidation catalyst by the HC sensor (130) and this contribution is made correlation with the activity of the oxidation catalyst. 6) Method according to claim 1, characterized in that to diagnose the amount of introduced hydrocarbons, is carried out post-injection. Process according to Claim 1, characterized in that the quantity of hydrocarbons introduced for the diagnosis is carried out using a separate HC hydrocarbon dosing system (160) in the gas channel of exhaust (50) upstream of one of the catalysts (70, 80, 110). 8 °) Method according to claim 1, characterized in that the amount of hydrocarbons introduced for diagnosis, is cold start of the engine (1). Method according to Claim 1, characterized in that if a threshold of the hydrocarbon accumulation capacity or a characteristic correlated with it is exceeded, a critical activity is recorded. for the oxidation capacity NO and a warning signal is issued and / or recorded in a fault memory of a motor control (140). 10 °) Application of the process according to one of claims 1 to 9, to a diesel particulate filter (120) as an indicator of the conversion capacity of the particulate filter (120), and in particular the diesel particulate filter (120). ) is combined with an upstream oxidation catalyst. 11 °) Device for monitoring an exhaust gas cleaning plant of a heat engine (1) composed of one or more catalysts (70, 80, 110) for converting and / or accumulating at least one component of exhaust gas of the heat engine (1), the catalysts being installed in the exhaust gas channel (50) of the heat engine (1), one of the catalysts (70, 80, 110) being a catalyst of oxidation device characterized in that by means of a diagnostic unit (150) connected in input to exhaust gas sensors (60, 90), and at least one temperature sensor (100) for determining the temperature or the temperature increase and / or an HC sensor (130) to determine the partially unburned hydrocarbons, downstream of the oxidation catalyst and with the aid of the signals of the diagnostic unit, it is possible to deduce a predictive diagnosis of the NO oxidation capacity of the catalysts (70, 80, 110), the hydrocarbons preferably at least from time to time in a targeted manner upstream of the catalysts (70, 80, 110) in the exhaust gas channel (50), where appropriate with the aid of special metering means controlled by the diagnostic unit (150). Device according to Claim 11, characterized in that at least one of the catalysts (70, 80, 110) comprises at least one accumulator component for partially unburned hydrocarbons, this component being formed from zeolite material. and the hydrocarbon storage capacity is reduced to temperatures at which sintering of the noble metals of the oxidation catalyst begins. 13 °) Device according to claim 12, characterized in that the adaptation of the accumulation capacity is adjusted by changing the silicon / aluminum ratio and / or the type of zeolites. Device according to Claim 11, characterized in that at least one of the catalysts (70, 80, 110) additionally has oxygen storage components.